(1) Field of the Invention
The present invention relates generally to environmental impacts of acoustic sources, and more particularly to quantitatively determine the acoustic impact of underwater acoustic sources on marine animals in a defined area of any body of water.
(2) Description of the Prior Art
Prior methods for determining acoustic impact on marine animals have either not quantitatively determined the number of animals effected, or if determining the number effected, have done so in a non-deterministic way. As an example, the Zone of Influence (ZOI) method determines the maximum range, or zone, around the acoustic source at which an animal is influenced under several criteria. The ZOI method establishes zones for such criteria as audibility, responsiveness, masking and hearing loss, discomfort, or injury. Although this method does give the distances at which marine mammals are affected by man-made noise, it does not determine the number of animals affected.
One present quantitative method, the Acoustic Integration Model (AIM), is able to count the number of animals influenced. It uses a statistical distribution of animals in depth and location combined with zones of influence. Inherent in the method is a Monte Carlo simulation that moves the animals in depth and location according to assumed behavior. Results are dependent on the average of many Monte Carlo simulation runs and on the accuracy of the input behavioral parameters. Each run of the Monte Carlo simulation provides a different result and can lead to incorrect attributions of the influence of model parameters because of this variance. In addition, running numerous Monte Carlo simulations is time consuming and costly. Further, the AIM method does not include the effects of the podding or herding tendencies of the animals.
Accordingly, it is an object of the present invention to provide a method to determine the acoustic impact of underwater acoustic sources on marine animals in a defined area of any body of water.
Another object of the present invention is to provide a method to determine the number of marine animals acoustically impacted by underwater acoustic sources in a defined body of water.
Still another object of the present invention is to provide a deterministic method for assessing the acoustic impact of underwater acoustic sources on marine animals in a defined area of any body of water.
Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings.
In accordance with the present invention, a method is provided to quantify and predictively estimate acoustic impacts to marine animals within a chosen area. The method begins with information collection, including information on the types of acoustic sources to be modeled, on the animal assemblages in the chosen area, on the environmental characteristics of the area and on the environmental regulations relevant to acoustic impacts in the area. An acoustic model, appropriate for the chosen area and its environmental characteristics, is then selected. As an example, the Comprehensive Acoustic Simulation System/Gaussian RAy Bundle (CASS/GRAB) model for horizontally stratified and range-variant environments would be an appropriate model for the East Coast Shallow Water Training Range (ECSWTR). Given the acoustic source characteristics and environmental characteristics of the chosen area, the acoustic model generates a source footprint of all sources to be located at the site. Depending on the impact criteria governing the area, the acoustic model expresses the acoustic propagation at the site as Sound Pressure Level (SPL), Sound Exposure Level (SEL), or other energy based criteria consistent with the governing regulations. The marine animal distribution, based on the most current information for marine animal assemblages in the geographic range of the area in question, is then overlaid onto the acoustic propagation at the site. The marine animal distribution is time-weighted to correspond with the proposed acoustic source usage, as well as short term and seasonal marine animal behavior patterns. The total number of impacted marine animals is then calculated. Impacts are calculated by species, source, scenario and season. The calculated number is then rounded upwards to the next whole individual, pod, or group, depending on the animals"" behavioral patterns and social structure. The acoustic test procedure, acoustic sources, source locations, or other criteria relevant to the number of marine animals impacted can then be modified to ameliorate the acoustic impacts.